Carbon dioxide (CO2) sensors are regularly used to measure the Indoor Air Quality (IAQ) in a controlled environment or the outdoor space to determine if it is suitable for introduction into the space via HVAC economizers or make-up air units. When used in IAQ applications, these sensors ensure the space receives the appropriate amount of outdoor air specified by ASHRAE Standard 90.1.

Equally important to many retailers, these sensors can also reduce the energy consumption of HVAC units. By limiting the amount of outdoor air introduced into space, the amount of conditioning associated with this air is also minimized. This so-called "Demand Controlled Ventilation" (DCV) is popular in many retail formats and other commercial buildings with variable occupancy.

In many cases, these IAQ sensors are combined into a single enclosure, as shown at right. These enclosures often include temperature, CO2, and relative humidity or dew point sensors in one convenient enclosure, which enables lower cost installation.